This invention relates generally to a device for determination of the absolute angular position of a turning component in relation to a fixed structure by means of a relative angular position sensor and, more particularly, to a system and procedure for measuring the absolute angular position of a steering wheel in relation to the frame of a vehicle containing such a device.
To facilitate the comprehension of the following for the reader, definitions are now given of the relative angular position, noted xcex8r, and the absolute angular position, noted xcex8a, of a turning component in relation to a fixed structure. Relative angular position xcex8r of the turning component is understood to be the angle separating the position of the turning component at a given moment from any initial position of the latter in relation to the fixed structure; this initial position can vary from one measurement to the other in relation to the fixed structure. Absolute angular position xcex8a is understood to be the angle separating the position of the turning component at a given moment from a reference position of the turning component, with this reference position being fixed in relation to the fixed structure.
Relative position sensors are known, consisting on the one hand of a multipole magnetic ring on which are magnetized several pairs of North and South poles, being mobile while rotating opposite a fixed magnetic sensor consisting of at least three sensing elements, respectively positioned opposite a main channel and xe2x80x9cturn cuexe2x80x9d reference channel and, on the other hand, a device for treating output signals produced by the sensing elements, designed to give a reference pulse per turn of rotation component integral with the multipole ring. This type of sensor is described in the document FR-A-2,769,088 under the name of the applicant. This type of sensor is entirely satisfactory for applications requiring only knowledge of the relative angular position of a turning component in relation to a fixed structure. On the contrary, this type of sensor does not make it possible to know the absolute position of the turning component when the latter makes several turns on itself.
Certain applications, such as the control systems for the path of a vehicle (of the ESP(copyright) type), require knowledge of the real angular position of the steering wheel in relation to a fixed median position in relation to the frame, in which the wheels of the vehicle are straight in relation to the latter. Sensors of the type described in the document FR-2,768,088 only make it possible to know the variations in the angular position of the steering wheel, but do not make it possible to know its absolute angular position corresponding to its real angular position. Absolute angle sensors of the optical or magnetic type and angle sensors of the multiturn type based on gears are known. The space required and the method of operating these types of sensors, however, require adapting the surrounding components, and do not meet the current requirements of automotive factories, especially in terms of space requirement and cost.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. The invention aims especially to resolve the above-mentioned drawbacks of the prior art, by proposing a device for determination of the absolute angular position of a turning component in relation to a fixed structure by means of a relative angular position sensor, which has a reduced space requirement and cost in relation to existing devices, which is relatively simple to operate, and which is easily adaptable to the direction support systems and/or to current safety systems of vehicles.
In one aspect of the invention, this is accomplished by providing a device for determining the absolute angular position xcex8a of a turning component in relation to a fixed structure by means of a relative angular position sensor xcex8r. A rotating mulipole magnetic ring, that may be integral with the turning component, is capable of making, jointly with the turning component, several turns around its axis of rotation from an angular position called the reference, said ring comprising a main channel and a reference channel called the xe2x80x9cturn cuexe2x80x9d channel, and with the main channel and xe2x80x9cturn cuexe2x80x9d channel being concentric on the magnetic ring. A fixed magnetic sensor, that may be integral with the fixed structure, is arranged opposite and away from a multipole ring by an air gap, and consists of at least three sensing elements, at least two of which are positioned opposite the main channel so as to produce two periodic electric signals A, B in quadrature. At least one of the three sensing elements is positioned opposite the reference channel so as to produce a reference electrical signal C called the xe2x80x9cturn cuexe2x80x9d signal in the form of an electric pulse per turn of the multipole encoder, with this pulse corresponding to an angular position called the xe2x80x9cturn cuexe2x80x9d angular position of the turning component in relation to the fixed structure, with the angular displacement between said reference angular position and said xe2x80x9cturn cuexe2x80x9d angular position being called xe2x80x9coffsetxe2x80x9d (noted xcex8offset). A counting means for counting pulses derived from A, B signals is capable of enabling the determination of the relative angular position xcex8r of the multipole ring and the variations of this relative angular position xcex8r.
This determination device also comprises a treatment device including detection means for detecting an angular position xcex80 of the multipole ring near said reference angular position. A resetting means for resetting the absolute angular position xcex8a of the multipole ring, detected by a detection means is capable of assigning, during detection of a pulse of the xe2x80x9cturn cuexe2x80x9d signal C, the offset value xcex8offset to the value of the absolute angular position xcex8a of the multipole ring in relation to its reference angular position. A determination means is provided for determining the absolute angular position xcex8a of the ring on all of the turns made by the turning component, from the offset value xcex8offset and variations in the relative angular position xcex8r. Moreover, this measurement is directly exploitable by the direction support systems, using the safety systems of a vehicle.
The foregoing and other aspects will become apparent from the following descriptionof the invention when considered in conjunction with the accompanying drawing figures.